The present invention generally relates to a double-face (or both-face or two-face) display device wherein data is displayed an both faces, i.e., a front face and a back face, of the display device generally in the form of a sheet depending on voltages applied thereto.
In recent years, active proposals and development works have been suddenly reported on a paper-like display (device) in which data can be electrically written and which is conveniently portable like paper without requiring a storing power supply. It is expected that the paper-like display will be future data-storing and supply means capable of replacing paper medium such as newspaper, magazines and books predominant at present, and a form of very light data processing means carrying a home page browser.
Such a paper-like display device is at least required to satisfy functions equivalent to those of paper medium as follows:
(1) being thin, light in weight and portable like paper medium,
(2) having a memory characteristic and not requiring a power supply for data storage, like paper medium, and
(3) being inexpensive, like paper medium.
Incidentally, having a structure comprising plural sheets of paper media bound along an edge, a book has a characteristic of allowing the reader to acquire data on other pages in a short period by a simple operation of turning over the pages (without requiring a troublesome operation of sequentially displaying data by successive scrolling on a simple display screen as in a conventional display device or apparatus), easily understand the contents by reading forward and/or backwards by turning the pages as desired and easily have a new conception based on the acquired and understood contents. In order to utilize this characteristic of a book in a paper-like display device, it is desirable to bind plural sheets of paper-like display devices along an edge into a book-like form (which will be referred to as an xe2x80x9celectronic bookxe2x80x9d hereinafter). In this case, the respective sheets of paper-like displays are caused to display a large volume of data downloaded from a data source. The above-mentioned functions (1) to (3) required of a paper-like display (device) are also important for realizing an electronic book by such paper-like displays.
Various proposals have been made on such a paper-like display, including the following as principal examples.
A microcapsule-type electrophoretic display (Nature, Vol. 394 [16], pp. 253-255, 1998),
A minute ball rotation-type display (Proc. of the SID, Vol. 118, 3/4, pp. 289-293, 1977), and
A cholesteric liquid crystal display (J. of SID, Vol. 5 [3], pp. 269-274, 1977).
Incidentally, in case where a display medium not having a clear threshold characteristic is used in such a paper-like display, it is desirable for the display to be driven according to an active matrix scheme. The active matrix scheme is currently predominantly adopted in a liquid crystal display device for notebook-type personal computers, etc., wherein each pixel is provided with a semiconductor switching device, such as a TFT or MIM, and voltages supplied to the respective pixels are controlled by the respective switching devices. This drive scheme has an advantage of obviating a crosstalk which is a problematic phenomenon encountered in the simple matrix drive scheme not having such switching devices at the respective pixels. As for methods of forming such switching devices, some proposals have been proposed as follows to form such switching device with an organic semiconductor material allowing the utilization of an inexpensive printing process instead of using inorganic semiconductors, such as amorphous silicon or polysilicon, incurring a high production cost, e.g., in
Nature, Vol. 394 [16], pp. 253-255, 1998,
J. in Proc. Materials Research Soc., B8.2, 1998, and
Science, Vol. 279 [17], pp. 383-384, 1997.
There has been also proposed a double-face display device wherein data is displayed not only on a single face but on two major surfaces of a generally sheet-form display device, e.g., in the following a representative examples:
a device formed by bonding two liquid crystal panels back to back (JP-A 02-265923), and
a polymer dispersion-type liquid crystal display device allowing independent displays on both surfaces of an intermediate supporting plate (JP-A 05-061024) as a proposal concerning a paper-like display.
FIG. 9 is a sectional view of a paper-like display (device) D6 disclosed in JP-A 05-061024 as an example of such a known paper-like display. The paper-like display D6 includes three substrates (or base plates) 1, 2 and 3 which are disposed in this order substantially parallel to each other and with prescribed gaps from each other. On respective surfaces of the central substrate (hereinafter called the xe2x80x9cintermediate substratexe2x80x9d) 2, display electrodes 4 and 5 and switching devices 6 or 7 are disposed, so that the display electrodes 4 and the switching devices 6 are electrically connected on one surface and the display electrodes 5 and the switching devices 7 are electrically connected on the other surface. Further, on the upper substrate 1 and the lower substrate 3, electrodes 20 and 21 are respectively disposed. Further, the two surfaces of the intermediate substrate 2 are respectively provided with control systems (not shown) so as to supply voltages to the display electrodes 4 and 5 via the switching devices 6 and 7, respectively, thereby allowing display of different data on both faces.
In the paper-like display D6 of the structure shown in FIG. 9, the intermediate substrate 2 is commonly used for two display faces, so that the total thickness and weight can be reduced to xc2xd to xc2xe compared with a case where the same amount of data is disposed on two sheets of paper-like displays. Further, if a plurality of such double-face paper-like displays are formulated into an electronic book, it becomes possible to advantageously observe double-sized picture areas simultaneously in an open state.
However, in the above-described type of paper-like display D6, the switching devices 6 and 7 are disposed on both surfaces of the intermediate substrate 2 so that the switching devices are formed by repeating a switching device-formation step twice which incurs an increase in production cost. Further, switching devices 6 or 7 on either one surface have to be formed in a state where the switching devices 7 or 6 on the other surface have been already formed, so that the switching devices formed in advance are liable to suffer from process damage, such as thermal damage, during the latter forming step.
Further, the control systems are formed independently on both surfaces, thus incurring a correspondingly higher production cost.
Accordingly, a principal object of the present invention is to provide an inexpensive double-face display device.
According to the present invention, there is provided a double-face display device, comprising:
a substrate sheet having a first surface and a second surface,
a first display medium disposed over the first surface,
a second display medium disposed over the second surface,
a first display electrode and a second display electrode disposed in association with the first display medium and the second display medium, respectively, and
a first switching device and a second switching device electrically connected to the first display electrode and the second display electrode, respectively, so that voltages are applied to the first and second display electrodes via the first and second switching devices, respectively, thereby driving the first and second display media to display data on both faces of the display device, wherein
the first and second switching devices are disposed on a common surface within the display device.
According to another aspect of the present invention, there is provided a double-face display device, comprising:
a substrate sheet having a first surface and a second surface,
a first display medium disposed over the first surface,
a second display medium disposed over the second surface,
a first display electrode and a second display electrode disposed in association with the first display medium and the second display medium, respectively, and
a first switching device and a second switching device electrically connected to the first display electrode and the second display electrode, respectively so that voltages are applied to the first and second display electrodes via the first and second switching devices, respectively, thereby driving the first and second display media to display data on both faces of the display device, wherein
the substrate sheet has a laminated structure including a first layer sheet and a second layer sheet, and
the first and second switching devices are disposed on a common surface between the first and second layer sheets.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.